The increasing thermal stresses in internal combustion engines, in particular in engines of passenger cars, increasingly require components thereof, such as for example the gas exchange valves, also abbreviated as valves, to also be cooled. For this, so-called hollow valves having an internal cooling medium are used.
From EP 2 541 000 A1 a method is known for the production of metallic hollow valves, in which by means of a corresponding die the valve is successively deformed, in particular its shaft is tapered.
From DE 10 2010 051 871 A1 a method is known for the production of metallic hollow valves for the gas exchange of an internal combustion engine, wherein the cavities of the hollow parts forming the valve are connected with one another and wherein these cavities are produced at least partly by electrochemical metal removal. For this, firstly the valve shaft is drilled through lengthwise, wherein subsequently the cavity is produced in the valve head as an enlargement bore transversely to the longitudinal axis of the valve shaft. By means of the described method, in particular the production of hollow valves is intended to be able to be simplified and, at the same time, their quality to be improved.
From DE 10 2012 209 187 A1 again a method is known for the production of a metallic hollow valve of an internal combustion engine, in which a bore is introduced into a forging blank of pear-shaped construction. A later valve head is then at least partially hollowed out by electrochemical removal, wherein subsequently the cavity which is produced in such a manner is filled by means of a support fluid and the hollow valve is closed. Hereby, the hollow valve can be produced at a comparatively favourable cost.
From DE 10 2011 077 198 A1 again a method is known for the production of a metallic hollow valve of an internal combustion engine with a valve head passing over into a valve shaft, in which a bore is introduced into the valve head and this is subsequently at least partly hollowed out by electrochemical removal. Hereby also, in principle the production of such metallic hollow valves is intended to be improved.
It is generally applicable to metallic hollow valves that these are lighter than solid valves and on filling with a cooling medium, such as sodium for example, they offer an improved heat dissipation. In Otto engines, a hollow valve which offers a particularly good heat dissipation leads to a shifting of the knocking limit and thereby to a particularly advantageous operation. The knocking designates the uncontrolled igniting of the petrol-air mixture owing to too high temperature and pressure. This leads to impacts in the internal combustion engine with high mechanical and thermal stresses, which ultimately impair the lifespan and the efficiency in a negative manner. If, however, the knocking limit can be raised, a higher compacting in the cylinder becomes possible, which leads to a distinct increase in efficiency in the combustion process and thereby to a higher performance with lower fuel consumption.